This invention relates to a circuit device for generating a synchronous signal to a steady wave component of an input signal, and, in particular, to such a circuit device which is useful as a circuit for developing a carrier wave synchronous to a pilot signal in the reception of a carrier suppression broadcast wave.
In certain cases, for example, in the reception of a broadcast wave, a circuit is required which is for providing a synchronous signal to a steady wave component, for example, such as a carrier wave. The synchronous signal is used for the detection of the broadcast wave.
A known synchronous signal generating circuit device includes two phase-locked loops, one of which comprises a voltage controlled oscillator (VCO), a phase comparator for phase comparing the output of the VCO with the input signal such as the broadcast wave to control the output of the VCO. The other, or the second, phase-locked loop comprises a second VCO, a second phase comparator for phase comparing the output of the second VCO with the output of the first VCO to control the output of the second VCO.
The AC component of the output from the second phase comparator is fed back to the first VCO to control the first VCO so that the phase variation of the output of the first VCO due to the phase variation component in the input signal may be suppressed.
The synchronous signal is obtained as the output of the second VCO.
The known synchronous signal generating circuit device stably operates under the input signal having the steady wave component of a greater amplitude than that of a phase variation component. But if the amplitude of the phase variation component is greater than that of the steady wave component, the operation of the device is not stable.
For example, in a carrier suppression single side band broadcasting system, the amplitude of the pilot signal is smaller than that of the side band wave signal. Therefore, the known circuit device is not useful for obtaining a synchronous signal to the pilot signal in the single side band broadcast wave.